Coded track circuit signaling system



July 4, 1944. s. N. wlGHT f 2,352,987

CODED TRACK CIRCUIT SIGNALING SYSTEM Filed May 2. 1941 7 Sheets-Sheet 1 s. N. wlcaH-r`4v y CODED TRACK CIRCUIT SIGNALING SYSTEM July 4 1944.

Filed May 2, 1941 7 Sheets-Sheet 2 lNvl-:NToR

ATroRNEY July 4, 1944. s. N. wlGHT CODED TRACK CIRCUIT SIIGNALING-SYSTEM Filed, May 2. 1941 v sxlee'a-sheifvv s ATTORNEY s. N. wlGH-r 2,352,987

CoDED TRACK CIRCUIT SICNALINC SYSTEM Filed May 42. 1941 7 sheets-sheet 4 July 4, 1944.

.ET OH July 4, 1944. s. N. wlGH-r I CODED TRACK CIRCUIT SIGNALING SYSTEM Filed May 2, 1941 '7 sheetsshea 5 lNvENoR ATroRN DnNcv-L July 4, 1944. s. N'. wlGHT CODD TRACK CIRCUIT SIGNALING SYSTEM Filed May 2, 1941 '7 sheets-snee: 6

m aum# w lNvENo 5 n N2 Vv@ Rw-ff, m@

AJuly 4, 1944. s. N. WIGHT CoDED TRACK CIRCUIT SICNALINC SYSTEM Filed Mayv A2. 1941 '7 Sheets-Sheet 7 r2 I SF2 n +V AISM Atv INVENToR BY 6' w by ATTORNY @@NVVIV mmm . b atl Patented July 4, 1944 CODED TRACK CIRUUIT SIGNALING SYSTEM Sedgwick N. Wight, Rochester, N. Y.,l assignor to General Railway Signal Company, Rochester, N. Y.

Application May 2, 1941, Serial No. 391,454

35 Claims.

This invention relates to signaling systems for railroads and it more particularlypertains to block signaling systems of the absolute permissive block type for single track railroads.

In the well known type of absolute permissive block signal systems such, for example, as in the system shown in my Patent No. 1,294,736, dated February 18, 1919, it is assumed that the passing sidings are located far enough apart to provide sum-cient safe braking distance for opposing trains to come to stopy after having encountered intermediate stop signals in the stretch of single track between sidings in case ofsimultaneous entry cf two opposing trains into such stretch of track. The braking distance must be provided beyond such intermediate signals because, under conditions of simultaneous entry of opposing trains into such stretch of track, the trains would encounter no caution indication to Warn the trainmen of the stop condition of the first of the intermediate signals to be encountered, and therefore the minimum distance between opposing intermediate signals must be double braking distance. The increased speed of the present trains and specific conditions encountered in present practice presents the problem as to how absolute permissive block signaling can be safely provided for short stretches of single track between sidings.

An object of the present invention is to provide an absolute permissive block signaling sytem employing Coded track circuits, without the use of line wires, that can be readily adapted to a short stretch of track as vwell as a long stretch of track between sidings to cause, in case of simultaneous entry into such stretch of track by two opposing trains, each of such opposing trains will encounter a caution signal prior to its leaving the siding section, and thereby have suflicient warning to bring the train to a stop short of the rst intermediate signal for that direction of traiiic. Such a mode of operation provides for safe operation of trains through a stretch of ,singie track between sidings having as few as two blocks. It is desirable, as provided by the present invention, that such restrictive caution indications be provided for opposing trains, but that less restrictive signaling be provided for following trains.

vIn accordance with the present invention each block has a coded track circuit, and each coded track circuit has at each end a code Vtransmitter anda code receiver. The various code transmitters can be defined as being of two different types, one type being a driven code transmitter,

- rate, is to provide that such carrier can transmit and the other type being an inverse code transmitter. A driven code as used in this descriptionlis a lcode repeated from a power driven coder or oscillator having the length of its impulses and the number of impulses per minute determined by the character of such coder or oscillator, while an inverse code is made up of impulses synchronized to energize a track circuit during the deenergized or 01T periods of a driven code transmitted from the oppositeV end of the track section to provide duplex code transmission for governing signals for both directions of traffic. In most coded track circuit systems ci this character the use of the inverse code is limited in that its code rate must be the same as the code rate of the driven code.

Another object of the present invention, using a driven code as a carrier ata given number of impulses per minute, is to vprovide for the transmission of any selected'one of several inverse codes, such codes being made distinctive because of the polarity of the impulses used and the frequency of occurrence of impulses of a particular polarity, the impulses of such particular polarity being spaced at times by a selected number of blank periods in the inverse code. By the number of distinctive inverse codes thus made available for use, it is provided according to the presentA invention that all desirable signal controls for a given direction of traffic can be transmitted through the track circuit in advance of each signal under thek various traino conditions by use of inverse codes.

Another object of the present invention, maintaining the impulsing of a track circuit to providea carrier for the inverse code at a given any selected one of several driven codes, such codes 'being made distinctive because of thepolarity of the impulses` employed for the carrier, and the frequency of occurrence of impulses of a lparticular polarity, the impulses of such particular polarity being spaced at times by impulses of the opposite polarity. It is therefore provided that all desired signal controls for a given direction of trafc can be transmitted through the track circuit in advance of each signal under the various conditions of traic by use of a driven code, and yet maintain a given nonpolar rate of transmission ofthe driven code` impulses so as to constitutea carrier forany selected one of the various inverse codes used for transmission through the track circuit for the opposite direction of traic.

Another object of thepresent invention is to provide impulse polarity selecting means for each of the driven and inverse code transmitters whereby impulses of one polarity in the code transmitted can be spaced by a selected number of impulses of the opposite polarity or, in some cases, by a selected number of blank periods in the code.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing the present invention in detail, reference will be made to the accompanying drawings in which corresponding reference characters are used to designate corresponding parts throughout the various iigures, in which like letter reference characters are used to designate parts having similar features and functions, such parts being generally made distinctive by reason of preceding numerals or by exponents indicative of the particular locations, functions or rates of code with which such devices are associated, and in which:

Figs. 1A, 1B, 1C, 1D and" 1E show diagrammatically the codes transmitted through the track circuits for the control of the various signals for this embodiment of the present invention in accordance with various assumed traffic condi-- tions; and

Figs. 2A, 2B, 2C, 2D, 2E' and 2F, when placed end to end, illustrate in detail the manner in which the present invention is applied to the control of signals for a typical stretch of track including a passing siding and a stretch of single track between passing sidings.

Rather than attempting to show the specific construction and varrangement of parts that would be employed in practice in accordance with the present invention, the illustrations are arranged to show diagrammatically in a simplified manner the circuits employed in order to facilitate the disclosure of the invention as to its mode of operation. Thus, symbols are employed in the conventional manner for the various devices. Relay contacts not shown directly beneath the relay with which they are associated can be readily identied as of such relay by the relay reference character above such contacts, such arrangement being provided in the conventional written circuit manner.

As a simplification of the illustrations, symbols are used in some cases to indicate connections to the terminals of batteries or other sources of electric current instead of showing all of the wiring connections to the terminals of such batteries. The symbols (-1-) and are therefore employed to indicate the connection to the positive and negative terminals respectively of suitable batteries or other sources of direct current, and the circuits with which those symbols are used always have current owing in the same direction. The symbols (B+) and (B-) are usedof the present invention, reference is made from time to time to functions common to all parts of a similar character by use of the letter reference characters without exponents or preceding numerals. It is to be understood that such a reference applies to any parts designated in the drawings by reference characters that are similar except for the preceding numerals or the exponents associated therewith.

With reference to Fig. 1A, the track layout chosen for this embodiment of the present invention consists of a main stretch of track divided into blocks and having passing sidings 23, 24, 25 and 25 spaced short distances apart by stretches of single track. Although only two blocks are provided between passing sidings, such, for example, as the blocks having track sections I-I IT and I2-I3T between the sidings 24 and 25, it is to be understood that a greater number of blocks can be provided between passing sidings in accordance with the requirements of practice.

It is assumed in this embodiment of the present invention that the passing sidings are connected at their ends by hand-throw switches to the main track, and that each track switch is provided with the conventional proper fouling protection and with a circuit controller for repeating the positions of the track switch.

A signal is provided for governing entrance to each of the blocks for each direction of traffic. That is, for example, the signals 8, It, I2 and I4 are provided for governing entrance respectively to track sections 8-9T, Ill-IIT, I2-I3T and I4-I5T for governing eastbound traffic (to the right). Asan example of the signals provided for governing west bound traic, it will be noted that signals I3, II, 9 and 'I are provided for governing entrance respectively to track sections !2-I3T, I IJ-I IT, 8-9T and 6--1T.

The symbols used for illustrating the various signals are to be considered as conventional symbols of the indications such signals can display or do display under certain trailic conditions, rather than illustrating the particular type of signa-ls employed, as it is to be understood that various types of signals can be used with the system provided by the present invention. The symbols employed do not take into consideration the provision of approach lighting for color light sign als as provided in Athis embodiment, but rather indicate the condition of the signals as if approach lighting were not provided. The signals employed in this embodiment of the present invention are of the type having individual color lamp units, orte unit providing a green indication for clear, another unit providing a yellow indication for caution, and a third unit providing a red indication for danger or stop. It is believed that it will be readily apparent to those skilled in the art how other well known types of signals such, for example, as searchlight signals, position light signals and semaphore signals can be employed.

Each of the blocks of this embodiment of the present invention has a single track circuit of the coded type, the coding being normally effective,

and a driven code being transmitted through each track circuit for the control of the west bound signal at its right-hand end, and an lnverse code being transmitted through each track circuit for the control of the east bound signal at its left-hand end.

relay, and one or more code receiving relays.

Atlthe: endzzof:4 each of :ther track circuits Where it is'desiredv 'tol use both plarities for ,trackvfeedsV the track battery hasvra"` center tap. .topr'vide for polarization of the track circuit. `.Acode following relay TA `ris connectedthe track circuit 'atfeachf end rof each-block. soi'. as7 to be operative-f in '.responseto l.theV energization ofits trackcircuit'fromthe op'pos'iteend of a particus lar polarity,'leach Aof fsuch frelays' TAI- havingla polar structure' to allow the picking .upf -of-fth'at relay only when it isA energized with suchpolarity: It is therefore provided'fthat each of the relays TA can be picked up only when 'the lowerurail" of themainr track of the track layout' fis''energized with a positivepolarity'from thevoppo'site end of the track circuit.` l 5"' f7 i '-fIn additionA to the code'receivingfrelay'TA connected Vin each end of "thetrackcircuits lis'fa neutral code following relay"-TBwhich is picked up on each impulse ofa code transmitted from' the opposite end of that track'circuit,irrespecr tive of the polarity of energization of suchv relay. Under conditions where a' neutral relay TB is not required Vexcept for approach@ control an ap# proach relay AP connected infseries with the track battery can be used as illustrated in Fig. 2E. Such approach relay is picked up only' when its track section is 'occupied by aftrain An impulsing oscillatordUCT isfprovidedffor the left-hand end of each of the blocksI for form#- ing the carrier impulses for the drivenand inversefcodes. Although the relays IBUCT are assumed-in this embodiment to be of theoscillatoryl type such, for example, as disclosed in thep'atent to P. N. Bossart,'`Patent No. 1,858,876, dated I May 17., 1932, it is to be understood that other types of impulsing means such as motor driven' impulsers can as well be used. Each oscillatoryy impulserV I8GCT used for thisembodiment of the present inventionv providesfoff and on periods of relatively equal length," and provides impulses at a given rate of 180 impulses per minute. `l 'I` n At the left-hand end of -each of the track cir-v cuits is a driven code transmitter comprising a stepping relay'bankfor selecting the polarity of the impulses to be transmitted` and a polar neu? tra] code repeater relay CP for pulsingthe track circuit to transmit impulsesof the polarities `sel lected by the stepping relay bank.'V Thev numbery of relays in a steppingbankis dependent upon the number'of different codes to be'selected for transmission under the varioustraflc conditions. That is, each of the stepping relay banks includes a code execution relay CEX`which directly repeats the oscillator for that end yo1 the track cir-I cuit for the transmission of a driven code composed of all positive'impuls'e's, and each fof the stepping relay banks vincludes :relays 98C fand 900A for causing therapplication of negative" impulses to the track circuit when it is'de'sirecl to transmit a code having alternately (-4-) and impulses. The numeralpreix 90 in the ref! erence characters 90C and 900A indicatesfthat' those relays are used'when it is desired to transmit a code having impulses' of a particular po` larity transmitted at a ratev of 90 impulses per minute. For certain of the track circuitswhen it is desirable to provide for the transmission of an additional code in which the (-F) impulses arel spaced by two impulses, the ste1cnpirig'relay- A bank also includes relays 60C and (illCAwhich are used to space the positive impulses in av manner as toprovide for thetransmission of*` impulses at the rate of' impulses: per

minute and yet space such impulses by `-char-'-4 acters inJ f'ordr to :maintain the ycarrier impulse rate of,` '180 impulses per minute.' 'llhei'stepping relays are all relativelyE quick acting=so that they can be picked up or,dropped away as required during single off or on periods.

`:At the right-hand 'fend of'eachof the'vtrack circuits-isan inverse code transmitter'compris-` inggfacv stepping relay.- bank f for .selecting".the polarityof.` the impulses" to be transmitted, :and an-finverse :code transmitter rrelay YCP y for; pulsing the: track 'circuit totrans'mit :impulses fduring the offlperiodspof the' driven'code of polarities selectedA by th'e stepping relay bank for that end ofthe track circuit. l Such relay bank includesA arelay CEX which isienergizeglfor eachfimpulse to be transmitted, relaysfSC and 90CAfor'proe viding the transmission of impulseslspaced Icy-blank; periods to provide afrate-offg'impul'ses per minute, and under conditions whenv another code is required; the 'stepping'i bank" for the:A inl verse code transmitter :includesf relays :EIJC- 'and 606A which provideV forf the transmission "of-4 (+1) impulses `spaced* two successive l blank lperiods ing theimpulses"receivedl vat-feach"end of each of the trackcircuit's, the .transformers TF being provided forthe energization of y'Hrrelays used for the control of thefsignals'fin `accordance with the traiiic': conditionsr immediately in 'advance thereof, andY such-y transformers being effective to provide energization for a tuned circuitrincluding' av condenser and a transformerTFA to provide forY the control of airelay D. `A relay D islpro-f vided foreach end of each of the blocks, and it is venergized only .uponV the reception ofa 180 T'code' composedof'all characters. In asimilar mannerY forcertainrof the block ends, an addi-f tional tuned circuit is -provid'ed'including a' transl former TFC and a condenser energizedfromthel transformer lTF atthat end of the track circuit for causing the energization of a relay HA, which is responsive -only 'to the reception of a` vcoole 'at the ratefofrSO impulses per minute.k Such relay is usedv primarily in ytheselectionv of codes for'transmission throu'ghvthe next adjacent block.Vv :"Astick relaylfS is' provided for v'each signal in orderto properly ydistinguish in the selectioncifv codes for transmission between opposing and folreasons'requiringy an additional time' elementin the operation of the system.

'It is'tobe understood that the selection' of' relays for'use'in thisemfb'odiment'of 'the present invention Vis made in .accordance with the .mostY i desirable 'operating- 'characterictics dependent in what capacitythefrelays are to be used That'is.' for example, the relays energized by tuned'v circuits are adjusted, as is the other'apparatus vassociated therewith, to lrespond :onlyto the desired frequency'fy and thef'relays for Vtlrestepping banks areadjusted"t`o 'provide `for lthe transmission. impulses of they most desirable length.' the' length" ofthe driven' code impulses' being comparatively equal to the length lof the off periodsand -thcy length ofthe inverse code impulses'being' 'slightlyl less tl'i-arifthr-:fv length of the v` driven code -oi"" periods for reasons to be hereinafter" pointed out.

Havingv thus' considered the apparatus provided for the system of lthe present invention, it -is ber` flieved that the mode of operation of the syst'emf 4 ais-sacar will best be understood upon considering hereinafter various typical operating' conditions which might be encounteredinpractice; f. OPRQTIQNZJ.

GcncTal.`-With reference :to Fig'. 1A, it will' be noted that, ywith :thev track layoutunoccupied by a train, a driven codeis 'transmitted through each vtrackzcircuit from left to -right for the control of West bound signals and an inverse'codeds transmittedfrom right 4to. left for the control-of eastbound signals, the direction-of transmission of the driven code being indicatedw-by the arrows having solid lines, and the direction of ltransmission of the inverse codes-.being indicated by the arrows having broken lines. f

, Under normal conditions-'when the track layout is unoccupied |by a tra-in, all signals are'clear (except-that approach lighting renders some of themnormally dark) because .of the' reception' of all impulses at :a rate per minute'the same as the rate of impulsing of the powerldriven oscillators which for this embodiment of the present invention'is assumed to be 4at a 1rate of 180 impulses `per minute. ditions illustrated in Fig.1A each of the signals is cleared becauseof the reception vof a code transmitted through the block' inv advancemade up of 180(+) impulses per .minute The west bound signals are cleared by a 180(+) driven4 code, and the east bound signals areclear'ed by a 180(+) inverse code. y i Y The next restrictive code used is a code havingalternately and `impulses or, in the case of an `inverse code, impulses spaced by single blank periods.- A ysignal receiving sucha code from the track circuit in advance is put `to caution, but such code having been received causes the transmission through the next block in the rear of an all code at a rate of 180 impulses per minute for the clearing of the next signalin the rear.

A further restrictive code is one having the impulses spaced 'by two impulses or, in thecase of an inverse code, impulses spaced `by two 'blank periods. A signal receiving such a code from a track circuit in advance is put to caution, but such code having been received causes the transmission through the next block in the rear of a codev having alternatelyv and impulses, or, in the case of.v an

inverse code, impulses spaced by'single'blank driven code, to provide a carrier for the trans.;

mission of an inverse code through the trackI circuit in the opposite direction. i i

Inasrnuch as the decoding means providedin accordance with the present invention for distinctively receiving the various codes is responsive only to the reception of impulses, the decoding is effective dependent upon the rate of occurrence of thev impulses in the code.'-

Thus, for the purpose of descriptionof the present invention, it can be said that a code-having all impulses is decodedas af180 code, a code` having alternately and impulses (or single blank periods for an inverse code) `is decodedas a 90 code, and a 'code havingr -two (1-.-)f im.-

Therefore, under the'conf pulses (or 'two blank periods forfaninversexcode) between .the v(+)y impulsesisa 60'code, the rates employedbeing the number) of (1+) vimpulses 'Der minute.

Normal conditions.-`With reference 'to Fig. 1A, it willibe'noted that each vof the .signals'fisconditioned to be clear lbecause of 'the reception of a 180 code for its ,controL the west bound signals beingv clear because of the reception of the 180 driven `codes and :the eastbound-signals being clear because of the reception of l18() inverse codes. Atthe left-hand end .of each of the'blocks', the impulsing :of the `track circuit' is eiTected by a code repeater 'relay CP which 4turn'repeats the code lexecution relayCEX for that endof the track circuit. When a 180 code is being transmitted, thek relay GEIL-follows the'circuit interrupting .oscillator `180CT associated therewith.

At Ythe right-hand.v end of each of the track circuits, under normal conditions', a relay-CP provides theirn-pulsing of the trackl circuit for the transmissionp'ofl an inverse code in accordance with vthe pulsing at a 1-80 rate of the code execution relay CEX lfor that end of. the track circuit. Such relay GEX gis pulsed by the neutral code following relay TB connected in the `track circuit at -that end of the block.

To consider more'specically, as a typical ex'- ample, how vthe 118,1) driven code is applied to a track circuit, with reference to Fig. 2A, under normalv conditions, the relay CEX follows the pulsing ofthe -relay |80CT by iits energi'zation during each on period upon the closing of a circuit extending from including frontcontact 4i] of the oscillator I8DCT,front contact 4l of relay 1H, and-lower windingY of relay CEX, to During each'period in which the relay GEX is energized, a circuit is closed to cause thepicking up of the 'code ytransmitterrelay SCP extending from (B+), including frontf'contact 43 of` relay "ITP, front contactv 44 vof relay CEX, winding of relay BCP, and/back contact 45 of relay BTB, to (CN). -It` will b e apparent as the description of `the invention progresses that the back contact 45 of relay STB in the circuit for relay SGP allows its energization for transmission of an impulse of al driven code only if there is a brief `period of deenergization ,of the track circuit immediately preceding. the transmission of each on period of a driven code.

. When relay BCP is picked up due to positive' energization, a circuit is closed to cause the picking up of the relays STB and STA (see Fig, 2B),

extending from -the positive terminal of the cen! ter tap track battery 4B (see Fig.' 2A) including' polar rcontact 41 of relay 8CP in its left-hand position, front contact `48 of relay BCP, the lowerv railof track section 8 9T,'back contact '49 of relay SCP; winding of relay STA, winding of relay 9TB, and upper rail of track section'S-ST to the center terminal of the track battery 4S. The positive or Vvnegative energization as used in the description ofl this embodiment of the present invention is to be understood as the polarity applied at the transmitting end of the track circuit to the lower rail of the track section.`

`When the-'neutral code following track relay 9TB is picked up during the on periods of the driven code, the closing of front contact 5B (see Fig. 2B) Ycauses the energizationof the repeater" l Such mode of operation provides a check of each inverse code 'relay 'STP which Ais suiflciently slow in dropping away to be maintained pickedup during the o periods of the code. Upon the picking up Vof the relay STA vduring eachon period, with therelay STP energized, energy isapplied to the transformer STF'by a' circuit closed from including front contact 5I of relay STA, upper portion of the primary -winding of transformer 9TF,-an front contact 52 of relay STP, to

The shifting-fof the contact I of relay STA causesa reversal of flux in the transformer STF because, when back contact 5I of relay STAV is closed during each olf period, energy flows through the primary winding of transformer-STF inV the opposite direction, such circuitbeing closed from including back contactl 5I-fof relay STA, lower portion of the primaryfwinding of transformer STFand front contact 52 of Vrelay STP, to It is therefore provided that-the reversal of polarity in accordance with the shift- Vin'gfof contact'5l causes quick reversals in flux in the` transformer STF and thus induces alternating current in the n secondaries of the transformer which' can be used for `the selective energization, inaccordance With the codes received, of the-relays SH, 9D and SHA, the-relay SH being energized upon the reception'of a 60, 90, or y180 code, relay SD' being energized by a tuned circuit upon the reception of a 180 code, and relay SHA being energizedby atuned circuit upon the -reception of a 90Y code. l

l The relay SH is astandard type direct'current neutral relay made-sufficiently slow in dropping away to Vride over the periods in the coding ofreduced energization. The contact 53 of relay STA f.

serves as a' rectier to I provide direct current energization for the relay SH. More specifically, when front contact 53 is closed energy-flows from the lower terminal of the secondary transformery winding 5d through a circuitv including i front contact 53 of relay STA, and winding of relayl 9H tothe center'terminal of Winding54. When back contact 53 of relay STA- is closedfen-v ergy flows through the winding of relayv 9H in the same direction by a circuit extending from the upper terminal of winding 54 including back contact `53, andr winding of relay SH to the center terminal of winding 54.

@Each reversal'of polarity in the transformer STF, when'a i180 code is being received, causes energy'to liow in the tuned circuit for the relay 9Din an vobvious manner, such tuned circuit including thesecondary winding 55 of transformerV STE'the vcondenser 56 and the primary winding Joffth'e transformer STFA. vvSuflicientenergy flows through thewinding of the relay 9D connected to the full-Wave r'ectier'l from the secondary vofthe transformer-S'I'FA to cause 'the energization -of the relay SD only upon thereceptio'n ofa 180 code. With the relays SH and SDpicked up, the circuits are conditioned to cause the-displayy of a clear indication by the signal 9, but, lunder normal'conditions, such signal remains dark because of the provision of YAapproach'lighting,

If the relay IUTP Were deenergized because of the approach of a train to signal 9, a clear Vindi'- cation Would be displayed by the energization of a circuit forthe'green lamp SG of signal 9, extending from (-1-), including back contact 61 of relay MITP, front contact- 68 of relay-SH, front contactBSjof'relay SD, andlarnp 9G, to j(-")`.

-Whe`n "the relay STB is picked up duringeach onWperiod'of the driven code received, the clos` ing of front `contact n58, under normalcondi'tion's, I

causes the picking up of the code execution relay CEX1 *upon the energizationof a circuit closed from..(-{.v), including l.front contact`58 of relay STB', front contactSS of relay ISH, and lower winding of relay CEX1, to The picking up offrlay GEX1 closes a circuit for the primary Winding of transformer S'I'FBV extending from (-1-), including' front contact 60 of relay. CEX1, front contact 4(il of relay STB, and 'primary winding of 'transformerSTFB to )..J'Iliebuilding n up of the flux of such transformerldoes not cause the picking. upn of the relaySCP, however, because such relayhas polar characteristics that cause it to respond onlyy upon the collapse of the iluxof the. transformer STFB. Thus, atthe end of each ofthe font periods, under normalconditions, the opening of front contact 6I of relay..9TB` causes the 'collapse of .the'flux in the primary Winding ofj'transformer. STFB, andthe induced vvoltage, in the secondary` winding of suchY transformer causes the picking up `of the inverse code transmitting relay. SCP for the transmissionV of animpulse of an inversecodexI f y p '.1 The picking :up of relay SCP duringeach off period 'of the.drivencode opens the .circuitgdescribed for .an' .on period ofwthedrivenzcode atfback-contact 4S for' the relays STBV andpSTA, and closes .aA circuit for the energization of the code followingtrack relays 8TA and 8TB; at ,the opposite end ofthe track circuit extending from the positive terminalfof `the center tap battery 62 .including front contact 63 of relay ISTR-.front contact 4S of relayv9CP,1oWer rail oftrack'section 8-9T, backfcontact I8.0i relay 8CP,.wind. ing of relay 8TB, winding of relay BTA, and upperrailof track section 8-9T, tothe.' center tap of thetrack batterylZ..v .As a resultof the energization ofthe neutral code following relay 8TB (see Fig. 2A) by veach inverse.- code impulse, the relay 8TP is picked up, by 4the energization, of lan obvious. circuit closed at jfrontcontact 45, and such relay is maintained picked vup by'its slow; drop aWaycharacteristics to ride over the foff impulsesof the inverse code received. .f y g1.,

Reversallofthe flux inthe transformer 8TB` is effected upon the ,picking `up of the relay'BTA duringthe on period' of the inversecodeupon the opening ofan. obvious circuit; yfor the lower portion of the` primary winding'. of, the1transformer I/a'tback contact 6.5` and the closing ofa circuit forV the upper portion-'of the primary winding of .that transformer extending from (-l-) including front, contact of.;relay 8TA,.upper portion 1 of the primary Winding of .the transformer STF, and front contact 66 ofrelay STP, to -The. reversal ofdilux in the' transformer 8TB' .upon .the reception'uof inverse code impulses causes the energizationcof the relaysBH and 8D in a Amanner comparableto thatdescribed in detail for the energization of the relays SH and; 9D for'theopposite end of Lthe'block. fIt is, therefore, provided that the transmission of a driven code through the track .section 8-9T conditions the signal S (see. FigyZB) so. that itwould be clear if approach lighting. were not `providedf'for that signal;.andat the same time, the .transmission of-an inverse code.fmadeup.of.all :impulses in` the oppositeidirection.. through f that track section conditions thev apparatus for control ofthe signal l8-(see Fig52A) 'so that Vsuch .signal can be cleared 'except for the-approach,y lighting control.

I t is provided in Ia similar-manner to that which has just been described:indetalthat, 4under normal conditions a driven code having all (-1-) impulses at a 180 rate is transmitted to the right through each of the track sections to cause the `clearing of the west-bound signal governingenverning entrance to that block so that such signa-l is clear except for approach lighting control. Y

Passage 'of east befand train-To consider the passage of an east bound train, it will be assumed that an east bound train A has entered track section 4- 5T as illustrated in Fig. 1B, but that the trackway in advance of such train' is unoccupied. The entrance of that traininto track section 4-5T causes the restoration to stop of the opposing signals 5 and1 in accordance with conventional absolute-permissive-block signaling practice, and the opposingsignals 9 and Il governing approach and entrance to the track section S-ST are put to caution. For the purpose of considering the movement of the east bound train through the track portion having its signal controlsillustrated in detail in Figs. 2A, 2B, 2C, 2D, 211.1' and 2F,'it will be assumed for the time being that the entrance of thetrain A into track sectionA- ST causes the transmission of a driven code having all impulses through the track section 6-1T. Upon the. reception of such, code at .the left-hand end ofthe passing siding 24, the relay. 1H is `dropped away because such relay is picked up only upon the reception of (-1-) impulses, but the track repeater relay 1TP for the right-hand end of the track section G-1T is maintained energized becausesuch relay is energized as a repeater of a neutral code followingrelay 1TB (not. shown) rather than a polar code following relay. Although the control ofv relays 1H, 1TB and 1TB is not shown, it Will be readily apparent that lthe. control of` such-relays is the same asis illustrated in; Fig. 2Ffor. the relay 13H, ISTP and13TB respectively..

With relay 1H dropped away and relay. 1TP picked up, a6() driven code is selected for transmission through the track section B-ST-to condition thesignal 9 to displayacaution indication.

Toconsider howA the 60.code made up of (-1-) impulses spaced by two impulses is formed, assume that .the steppingrelays are fall deenergized during an oil period in thecoding. Under such conditions, the shifting of contact '40 of oscillator. IBBCT .(seeFig. 2A) to its upper position closesv acircuit to cause thepicking up of the relay BBC, extending from (-1-) including front contact 40. ofthe oscillator` IBUCT, back contact 4I.. of relay 1H, lower Windingof` relay 90C land back contact 1I] of relay CEX, to When relay 90Cr is picked up, a stickcircuit is closed for its upper winding extending from (-1-), including back contact 12 of relay CEX, front contact 16 of relay 90C, and upper winding of relay 90C, to ).v Upon the shifting of the contact of the oscillator IBUCT toits, lower position, a circuit is closed. to cause the picking up of relay SUCA extending from; (-1-)including back contact 4U of oscillator IUCT, front contact 1I of relay 90C, and lower winding of relay 90CAto Upon thepicking up of that relay a stick circuit is closed. for its Vuppenwinding extending from (-1-), including, back contact 12 of relay CEX, front contact 13 of relay 900A, and; lupper winding of relay 90CA,.to.(. When contactlAU lor oscillator IQUCTgshifts again, the closingof frontco'ntact 40 causes the pick-ing upof relay 60C by the energization of a circuit extending from (-1-), including front contact 40 of oscillator IMK-ST1?, back' Contact 4I lof relay 1H, front contact 14 of relay BOCA, back contact 15 of relay 1S, lower winding of relay SBC, and back contact 10 of relay CEX, to Upon the picking up of relay 60C, a stick circuit is closed for that relay extending from (-1-), including back contact 12 of relay GEX, front contact 11 of relay 60C, and upper jwinding of relay 60C, to

`The next time the contact 4,0 of the oscillator IBDCT shifts to its lower position, a circuit is closed to cause the picking up ofthe relay BDCA extending from (-1-), includingback contact 40 of oscillator ICT, frontcontact 18 of relayA 60C, and lower winding of, relaylCA, to The picldng up of relay 600A closes a stick circuit for that relay extending from (-1-), including back contact 12 of relay CEX, front contact 1 9 of relay GOCA, and upper winding of relay GOCA, to

`When-the contact 40 of the oscillator |80CT is again rnoved to its upper position a circuit is closed to cause the picking up of the code execution relay CEX, extending from (-1-), including front contact 40 of oscillator IBGCT, back contact 4I of relay 1H, front contact 80 of relay BECA, and lower winding of relay CEX, to When relay CEXis picked up, a stick circuit is closed for that relay to maintain it energized until the shiftingprof contact 40 of oscillator IBUCT to its lower position, extending from (-1-), including front Contact of oscillator IBOCT, back contact 4I of relay 1H, front contact 8l of relay GEX, and upper Winding of relay CEX, to Upon the` picking up of relay CEX the relays C, 900A, 60C and GOCA are dropped away because their stick circuits are opened at back contact 12 of relay CEX. o The pick-up circuits for the relays `MICA and GBCA are open at that time because those relays are picked up only when the contact `4l) oscillator I80CT is in its lower position, and thepick-up circuits for relays 90C and 60C are open at that time because of the opening of back contact 10 of relay CE'X. The next time the contact 40 of the oscillator I80CT shifts in its position, the relay CEX is dropped-away to complete the restoration of the stepping relays because of the opening of its stick circuit at front contact 40, its pick-up circuit having a1- ready been opened upon the restoration of the relay lSIRIA. I

From the above description of the mode of operation of the steppingv relay bank, it willbe noted that the cycle of operation described included three periods in which lthe contact 40 was assumed to have been operated to its upper posi-v tion. During the first of such periods the' relay 90C is picked up, and the other stepping relays remain dropped away. Thusunder such conditions, a circuit is closed for` the energization of the polar-neutral relay BCP -for 'transmisison of a impulse, extending from (B including front contact 82 of relay 90C, back contact 83 of 4relay 900A, Aback contact 44 of relay CEX,

Winding of relay 8CP', Jand back contact '45 of relay B'II'B, to (CN). The picking up of relay BCP with its polar Contact o'pera'tedut@ a righthand position in accordance with such energization Acauses the enegization of thev code following ,track relays STB and GTA at thelopposrite end oiv the track circuitby a circuit extending -from theenter tap of .track battery 4 6 Aincluding-the upper rail of tracksection -VS'VI, Winding of relay STB (seeFigg2B), winding of relay STA, back contact 4S of relay SCP, lower rail of track section B-ST, front contact 48 of relay 8CP (see Fig. 2A), and polar contact 41 of relay 8CP in a right-hand position to the negative terminal of track battery 46. The polarity of energization of the relay STA in the circuit just described is such as to cause it to be unresponsive to the impulse. The neutral relay STB is of course picked up, irrespective of its polarity of energization.

When the contact 40 of the oscillator |80CT shifts to its lower position following the picking up of relay 90C, the picking up of relay 90CA opens the circuit just described for relay 8CP at back contact 83, to cause that relay to drop away for the initiation of an olf period in the code applied to the track circuit of track section 8-ST. Such oli period is terminated, however, upon the picking up of the relay 60C responsive to the shifting of contact 40 of the code oscillator |80CT to its upper position. The relay 8CP is then again energized to cause the transmission of a impulse in the track circuit. The circuit closed for the energization of relay 8CP extends from (B including front contact 82 of relay 90C, front contact 83 of relay SSCA, front contact 84 of relay 00C, back contact 85 of relay 600A, back contact 44 of relay CEX, winding of relay P, and back contact 45 of relay STB, to (CN). The shifting of Contact 40 of oscillator |80CT to its lower position next causes the picking up as hasy been described of the relay BBCA, and such l relay in picking up opens the circuit just described for relay SCP at back contact 85 to cause its release to initiate an off period in the code beine' transmitted through the track circuit. Such o period is terminated upon the picking up of the relay CEX responsive to the shifting of contact 40 to its upper position, and upon the picking up of relay CEX under such conditions, with the relay ITP energized, a circuit which has been described is closed to cause the picking up of the polar-neutral code transmitter relay 8CP with its polar contact operated to a left-hand position to close the track circuit as has been described lfor the transmission of a impulse. The (-l) impulse is terminated upon the dropping away of the relay 8CP when the relay CEX is dropped away to complete the restoration of the relays of the stepping relay bank to their deenergized conditions. A cycle of operation has, therefore, been completed in which three impulses have been applied to the track circuit, the first two impulses being of negative polarity, and the third impulse being of positive polarity. It is to be understood that the cycle of operation just described is repeated continuously to cause the transmission of polar impulses so arranged as to provide for the transmission of (-l) impulses evenly spaced at a rate of 60 impulses per minute.

With reference to Fig. 2B, consideration will be given to the reception of a 60 code. Although the windings of the relays STB and STA are both energized during each impulse of the code received, irrespective of polarity, the relay STA is picked up, due to its polar characteristics, only upon the reception of impulses, while the neutral relay STB is picked up for each impulse of the code received irrespective of polarity. It is, therefore, provided that the contact of relay STA is pulsed at a 60 rate lto cause the energization of the relay SH in a manner which has been described, butthe relay SD is dropped away because its tuned circuit which has been devscribedis tuned for only a code at a 180 rate. The relay SHA remains in its deenergized position because its tuned circuit for its energization is responsive only to the reception of a S0 code formed' by alternately and impulses,

'It is, therefore, provided that, were the approach lighting effective for the signal 9, a circuit would be closed for the yellow lamp SY of such signal for a caution indication extending from (-l-), including back contact 6l of relay |0'I'P, front contact 68 of relay SH, back contactBS of relay 9D, and lamp SY of signal S, to

It will be noted that the reception of a 60 driven code at the right-hand end of the track section 8 -9T in no way aiects the transmission of an all (-1-) inverse code back through the track circuit because the iinpulsing of the inverse code is dependent upon the neutral code following relay STB which is energized during each impulse, irrespective of the polarity of such impulse. It is, therefore, provided under the assumed trafc conditions, that a 180 inverse code is transmitted through the track section S- ST to condition the signal 8 so that it will clear, dependent upon the approach of the train A to provide approach lighting.

It will be noted from the conditions that have just been described that the relay 9H is energized, and relays SD and SHA are deenergized, and the track reepater relay STP is energized in an obvious manner in accordance with the reception of a 60 code at the right-hand end of track section 8-ST. It is, therefore, provided with the relays thus conditioned that a 90 code will be transmitted through the track section 0| ET to govern the caution indication of signal (see Fig. 2D). Inasmuch as the code transmitted under such conditions is a 90 code rather than a 60 code, the stepping relays 60C2 and E0CA2 (see Fig. 2C) remain deenergized during the transmission of the 90 driven code.

To consider a cycle of operation of the stepping relay bank for the left-hand end of track section |0| IT, assume the stepping relays all to be momentarily deenergized during an 01T period of the driven code following the transmission of a impulse. Upon the shifting of contact |03 of the oscillator |80CT2 to its upper position, a circuit is closed to cause the picking up of relay 9002 extending from including front contact |03 of oscillator |80CT2, back contact |04 of relay 9D, Iback Contact |05 of relay SHA, lower winding of S0C2, and back contact |06 of relay CEX2, to Upon picking up of that relay a stick circuit is closed for its upper' winding including back contact |01 of relay CEX2, front contact |08 of relay S002, and upper winding of relay S0C2, to

When contact |03 of oscillator |80CT2 shifts to its lower position, a circuit is closed to cause the picking up of the relay S0CA2 extending from including back contact |03 of oscillator |CT2, front contact |09 of relay S002, and lower winding of relay S0CA2, to

Due to the energized condition of the relay STP for the adjoining track section, a circuit is closed upon the shifting of contact |03 to its upper position for the energization of the code execution relay CEX2, such circuit extending from including front contact |03 of oscillator |80CT2, back contact |04 of relay SD, back contact |05 of relay SHA, front contact ||0 of relay 1S0CA2, front contact of relay STP, and lower winding of relay CEX2, tov(-l). ,l The picking up` of relay CEX2 causes the release of relays BBC2 and 90CA2 by opening their stick circuits at back contact |01 and opening the pick-up circuit for relay 90C2 at back contact |05. The release of relay 90C2 opens the pick-up circuit just described for relay 900A2 at front contact |09. The relay CEX2 is held up, however, until the shifting to the lower position of Contact |03 of oscillator ||l|lCT2 by a stick circuit for its upper winding closed from (-1-), including front contact |03 of oscillator |80CT2, Aback contact |04 of relay 9D, back contact |05 of relay SHA., front contact I3 of relay CEX2, and upper winding of relay CEX2, to The restoration of relay GEX2 upon the shifting of contact |03 of oscillator |80CT2 to its lower position completes the restoration of the stepping relay bank to complete a cycle of operation in which the relays 60C2 and 60CA2 remain idle and relays BBC2, 80CA2 and CEX2 are used for causing alternately (-l-) and impulses to be applied to the track circuit.

The polar-neutral transmitter relay |CP is pulsed alternately with one polarity and then the other in accordance with the operation of the stepping relay bank to apply alternately and impulses to the track circuit |0| |T, That is, upon the picking up of the relay 9002, the relay |0CP is picked up withv yits polar contacts operated to a right-hand position because of negative energization by a circuit extending vfrom (B including front contact H4 of relay SDCZ, back contact ||5 of relay 90CA2, back Contact IIB of relay CEX2, winding of relay lllCP, and back contact ||1 of relay IUTB, to (CN).

When relay |0CP is picked up with its polar contact operated to a right-hand position, a impulse is applied to the track circuit of track section |0| IT to cause the energization of the windings of relays HTA and IITB (see Fig. 2D) by a circuit closed from the center terminal of track battery ||8 (see Fig. 2C) including the upper rail of track section |0-||T, winding of relay ITB, winding of relay HTA, back contact ||9 of relay HCP, lower rail of track section |0- ||T, front contactl |20 of relay |0CP, and polar contact |2| of relay |0CP in a right-hand position to the negative terminal of track battery I8.

When the relay SllCA2 is picked up upon the shifting of contact |03 of oscillator |80CT2 following the energization of relay 90C2, the impulse applied to the track circuit is terminated because of the opening of the circuit for relay |0CP, at back contact ||5 of relay 90CM. The next time the contact |03 of oscillator |8|1CT2 shifts to its upper position the picking up of relay ClilX2 terminates the ol period of the driven code being transmitted through tra-ck section Ill-HT by causing the energization of relay |0CP with positive polarity. Relay IUCP is energized under such conditions by a circuit closed from (B+) including front Contact H of relay CEXZ, winding of relay |0CP, and back contact ||1 of relay |0TB, to (CN). The shifting of polar contact |2| of relay IGCP causes the energization of the track circuit for track section Ill-I iT with a positive polarity, the track circuit energized being the same as has been described except that the positive terminal of track battery I8 is connected in the circuit instead of the negative terminal due to the polar contact |21 of relay |0CP being operated to its left-hand position.

At signal (see Fig. 2D), the reception of the 90 code causes the pulsing of contact |22 of the cod-e following track relay HTA at a 90 rate because such relay follows only the impulses, and as a result of the pulsing of that Contact the relay HH is maintained picked up in a manner comparable to that which has been described in detail for relay 9H, the circuit for relay HH including back contact |23 of the stick relay |2S for the opposing signal for purposes to be more readily apparent as the description of the invention progresses.

In accordance with the l'reception of the 90 code, suflicient energy flows through the tuned circuit for relay IHA including secondary winding |24 of transformer ||TF, condenser |25, and primary winding |26 `of transformer IITFC to cause the relay ||HA to be operated to its energized position. The relay IID is deenergized because its circuit is tuned only to a rate.

With the relays for the control of signal conditioned as has been described, it is provided that signal would display a yellow caution indication if the approach lighting contact |34 4of relay |2APP were closed. Under such conditions the yellow lamp of signal would be illuminated by the energization of a circuit closed from (-4-), including front contact |34 of relay |2APP, front contact |35 of relay IH, back ccntact |36 of relay ||D, and lamp ||Y, to

The neutral code following track relay ||TB follows each impulse of the driven code applied to track section |0-| |T, and closes an obvious circuit at contact |21 to cause the energization of the track repeater relay IITP, such relay remaining picked up during the off periods of the code received. The pulsing of contact |28 of relay IITB causes the picking up of relay ClllX3 during each on period lof the driven code received, by the energization of a circuit extending from (-l-), including front contact |28 of relay ||TB, front contact |29 of relay |2D, and lower winding of relay CEX3, tn Such energization of the relay CEX3 causes the energization of the relay ICP during each of the oi periods of the driven code for the transmission of an impulse for the inverse code in a manner comparable to that which has been described in detail with reference to the control of the relay 9CP.

Upon the picking up of the inverse code transmitter relay ICP during each oi period of the driven code, a circuit is closed for t-he transmission of a (-1-) impulse through the track circuit of track section |3| |T extending from the positive terminal of track battery |30 including back contact |3| of relay HS, front contact |32 of relay |2H, front contact ||9 of relay HCP, lower rail of track section |0-||T, back contact |20 (see Fig. 2C) of relay |0CP, winding of relay |0'I'B, winding of relay |0TA, and upper rail of track section I- I IT to the center terminal of the track battery |30 (see Fig. 2D).

It is provided at the location of signal |0 (see Fig. 2C) that the reception of a 180 inverse code causes the pulsing of contact |31 of relay |0TA at a 180 rate to effect the energization of the relay |0H in a manner comparable to that described in detail with reference to the energization of relay 9H, and to cause suicient energy to ilow in the tuned circuit of relay |0D to cause the picking up of that relay. Under such conditions the signal |0 displays a green clear indication because of the energization of a circuit for the green lamp |0G of that signal extending from including front contact |38 of relay lill-I, front contact |39 of relay 10D, and lamp IGG, to The signal |0G has been illustrated as being a'asacs'? sion through the track section |2|3T for the' control of signal I3. To apply such code, with reference to Fig. 2E, the relay CEX4 is picked up each time the contact |50 of oscillator |80CT4 is closed. The relay CEX4 is picked up under each of such conditions by the energization of a circuit extending from including front contact |50 of oscillator |80CT4, front contact |5| of relay IHA, and lower winding of relay CEX4, to

The driven code transmitter relay |2CP is picked up with itsA polar contact operated to a left-hand position for the application of a impulse to the track circuit ofv track section |2-|3T each time the relay CEX4 is picked up. Relay |2CP is picked up under such condition by the energization of a circuit closed in accordance with the energized condition of relay IIH, extending from (B+), including back contact |52` of relay |2S, front contact |53 of relay I IH, front contact |54 of relay CEX4, winding of relay |2CP, and back contact |55 of relay |2TA, to (CN).

Upon the picking'up of relay |2CP with its polar contact operated to a left-hand position, a circuit is closed for the positive energization of the track relays at .the opposite end of the track section, extending from the positive vterminal of track battery |56, including polar contact |51 ol relay |2CP in a left-hand position, front contact |58 of relay |2CP, lower rail oi track section |2-|3T, back contact |59 (see Fig. 2F) of relay |3CP, winding of relay |3TA, winding of relay |3TB, upper rail of track section |2-| 3T, and winding of approach relay IZAP (see Fig. 2E.) to the center terminal of track battery |56. The approach relay |'2AP has such operating characteristics as to provide that it remains dropped away except when an abnormal amount of current flows through the track circuit for track section |2-I3T due tothe presence of a train in such track section. K

With reference to Fig. 2F, the relay |3TA is picked up during each impulse of the code received as the code received is a 180` rate, and the pulsing of contact |60 of that relay provides for the picking up of the relays |3H and |3D in a manner comparable to that heretofore described in detail for the picking up of the relays 9H and 9D. With relays ISH and |3D picked up, the signal I3 `is cleared 'upon the closing of a circuit for the green lamp ISG of that signal extending from (-1-), including frontv contact 16| of relay I3 H, front contact |62 of relay I 3D, and lamp I3G, to (v In accordance with the pulsing of contact |63 of the neutral code following relay |3TB at a 180 rate, the relay CEX5 isenergized during each on period of the driven code received for the transmission of a impulse during each off period of the driven code. Under such conditions the relay CEX5 is picked up during each on period ofthe drivencode received upon the closing of front contact |63 of relay |3113 for the energization of a circuit extending from (-l),

relay CEX5, to- In accordance with the picking up of relay CEX5, the closing of front Contact |65 conditions the circuit for the inverse code transmitter |3CP so that such relay will be gization of circuits comparable to those whichl picked up upon the opening of front contact |66 of relay |3TB in a manner heretofore described in detail with respect to the control lof relay 9CP.

When the inverse code transmitter relay |3CP is picked up during each of the oli periods of "the driven code for the transmission of a 180` inverse code, the track circuit of track section |2--I3T is energized with positive polarity by a circuit closed from the positive terminal of track battery |61 including front'contact |59 of relay contact |58 (see Fig. 2E) of relay |2CP, winding of the code following track relay |2TA, and upper rail of track section |2|3T to the negative terminal of track battery |61.

The pulsing of contact |58 of relay |2TA upon the reception of a 180 inverse code transmitted through the track section |2-I3T causes the picking up of relays |2H and |2D by theener-` have been described in detail with reference to the control of relays 9H and 9D, the circuit for relay |2H including back contact |69 of relay IIS which is the stick relay for the opposing msignal for a purpose to be hereinafter .pointed *the energization of the green lamp IZG of signal I2 extending from (-I-), includingback contact |10 of relay II'IP, front contact |1| of relay I2H, front contact |12 of relay |2D, and lamp |2G,

including front contact |63 of relay |3TB, frontp A contact |64 of relay I4D, and lower winding of It has therefore been described in detail how the signal indications as illustrated in Fig. 1B are provided in accordance with the presence of the east bound train A in track section 4-5T, assuming the track layout in advance of such 'train to be clear, rather than tobe occupied by the train B as illustrated. To consider the sig-e nal indications provided in accordance with further progress of train A through the ltrack lay'- out, it will be assumed that the train A 'enters track section 6-1T as illustrated in Fig. 1C, but it will also be assumed that the track layout in advance of the train A is clear instead of being occupied by the train B as illustrated.

Upon comparison of Figs. 1B and 1C, it will be noted that the entrance of the train A into the block immediately in the rear of the entering signal 8 changes the driven code transmitted through the track section 8-9T from a 60 code to a code composed of all impulses to cause "signal 9 to indicate danger. It is provided, however, that such change in the transmission of code through track section 8-9T does not affect the transmission of the code through the track section |0| IT in the rear of signal 8 for the caution indication of signal II. Such being the case, the signal indications will remain as they have been described above, except for the con-I ditioning of signal 9 to` provide a danger infcuit Which has been described for the application of impulses of the 60 code previously transmitted through track section 8 9T at front contact 43, and changes the polarity of such impulses from to by closing a circuit for the code transmitter relay 3GP duringy each period when relay CEX is energized extending from (B including back contact |13 of relay 1T?, back contact |14 of relay 1S, front contact 44 of relay GEX, winding of relay BCP, and back contact 45 of relay STB, to (CN) The energization of relay SCP by such polarity causes to be picked up with its polar contact operated to a right-hand position to cause the transmission of a impulse through the track circuit in place of each (l-) impulse as heretofore described in the transmission of a 60 code.

As a result of changing the code transmitted through track section 3 9T to a driven code having all impulses, the polar code receiving relay STA (see Fig. 2B) for the right-hand end of the track section 8 ST fails to pulse, and therefore causes the droppinfy away of the relay H to open the circuit for the yellow lamp of signal 9 at front contact (i9, and to provide that the red lamp SR of signal 9' Would be illuminated,

vif the approach lighting contact 61 of track repeater relay |0TP were closed, by a circuit ex.- tending from including back contact 61 of relay IQTP, back contact i'of relay 9H, and,

lamp 0R, to It will be noted that the reception of the driven code consisting of all characters at the right-hand end of track section 8 9Tv maintains the relay QTP energized because such relay is energized in accordance with the pulsing of contact 50 of the neutral code following relay STB which follows the code formed of all impulses. This being true, it will be noted that the stepping continues as has been described of the stepping relays for the left-hand end of track section |0 ||T to continue the transmission of a 9() code through such track section because such code is selected to be applied by front Contact of relay STP which is maintained closed. Such contact when closed shunts out, so to speak, the relays GGCZ and 600A2 of the stepping relay bank to provide for the transmission of a 90 code.

To consider further progress of an east bound train through the track layout, assuming the track layout in advance of such train to be un.- occupied, a condition will be considered in which the train A has entered the track section 8 9T as illustrated in Fig. 1D. The entrance of the train A into the track section 8 9T of course removes the driven code composed of all impulses as illustrated in Fig. 1C for the track section 8 9T, and the removal of such code changes the code transmitted through track section l|T from a 90 code to a 60 code. The reception of such code at the right-hand end of the track section maintains the conditioning of signal to display a caution indication, but causes a change to be effected in the transmission of codes through the track section |2 |3T in the rear of signal from a 180 code to a 90 code, and thus causes the signal, I3 to display a caution rather than a clear indication. Such caution indication is desirable as it will be hereinafter pointed out more specically in providing protection for trains in case of simultaneous entry into the short stretch of track extending between sidings.

Assuming the train A to have entered the track section 8 9'1 as illustrated in Fig. 1D, and assuming the track layout inl advance of the train to be clear, the code following relays GTA and 9TB (see Fig. 2B) are both inactive for the righthand end of the track section 8 0T because of the presence of the train, and the track repeater relay STP is dropped away because of the contact 50 of relay STB becoming inactive.

In accordance with the drop-away of relay STP, the code transmitted through track section |0 IT is changed from a 90 to. a 60 code upon the shifting of contact (see Fig. 2C) of relay STP in the circuits for the relays of the.` stepping relay bank associated with the left-hand end of such track section.

It is therefore provided, during a cycle of operation of the stepping relay bank, that the shifting of contact |03 of oscillator ISEICT2 to its upper position following the period in which. relay 90CA1 is picked up, causes the picking up of the relay 6002 by the energization of a circuit extending from includingfront contact |03 of oscillator |CT2, back contact |04 of relay 9D, 'back contact. |05 of relay 9HA,.front. contact |0.of relay 9.0CA1, back contact of relay STP, back contact |15 of relay 9S, lower Winding or"` relay 6UC`2, and back contact |06 of relay CEX2 to An obvious stick. circuit is. closed aty front contact |16 of relay 60C2 to. maintain it energized until the code execution relay CEX2 is picked up. The picking up of relay 60C2 conditions a pick-up circuit for relay 60CA2 whichis closed upon the shifting of contact |03 of oscillator |'80CTZ to its lower position, such circuit.

extending from (-l), including back contact |03-- of oscillator |80CT2, back contact |11 of relay BBC2, and lower winding of relay 60CA2, to 'Ihe picking up of that relay closes an obvious stick circuit at front contact 2|3 to maintain it picked up until' the code execution relay CEXz ispicked up for the transmission. of a (+V) impulse.

The picking up of relay lCA2 conditions a circuit for the relay CEX2 so that such relay can be picked up upon the shifting of contact |03 ofoscillator |80CT2 to its upper position to close a circuit extending from including front contact |03 of oscillator |00CT2, back contact |04 of relay 9D, back contact |05 of relay 9-IIA,.

front. contact |18 of relay 60CA2, andlower wind.- ing of' relay CEX2, to that relay closes its stick circuit at .front corttact ||3 in a manner which has been described', to cause the relay toremain picked up for the transmission of. the impulse while the other stepping relays are being restored in.. a manner.y

which has been described.` It is, therefore., pro.- vided that the front contact IIB. of relay CEX2 is closed. for every third impulsev transmitted. through. the track section, |0` ||T`,. the.rst im, pulse being in accordance witl1.theA polarity of energization of` relay IOCP. upon. the Vpicking up of relay C2, and the second. impulse being in accordance with the energization of relay IOCP upon the lpicking up offrelay 60C? byl a circuit extending from. (B1-) including front. contact, |14 of relay 90\C.2,f'ront. contact H5 of relay. 00CA2', frontcontact. |13 of. relay 6002, back contact |81. of relay 60CA2, back contact |I6..o relay ClilX1",'.windir1g` of relay. |0'CP', and, back contact ||1 of. relay |0TB'to.-(CNf)..

In accordance with the receptionatthe righthand. endot track section I0 IT of-a.60 rather. than. a 90 code,. the relay Ill-IA.. (see Fig.- 2D) whichv is energized by. a circuit...tuned-.tothe 90.l code isdroppedl awaybut. the relay. His. main- The picking up of.

tained energized by the 60 code to condition the signal for the display of a yellow indication as hasbeen described. The restoration of the relay I IHA, however, causes the code transmitted through track section I2-I3T for the control of signal |3 to be changed from a 180 to a 90 code in accordance with the opening of front contact |5| of relay IIHA and the closing of back contact |82 of that relay in the circuits for the stepping relay bank for the left-hand end of that track section.

vIt is therefore provided that, following a period in which the stepping relays for the left-hand end of track section I2-I3T are momentarily deenergized, the shifting of contact (see Fig.`

2E) of the oscillator |80CT4 to its upper position causes the picking up of theA relay 9004 by the energization of a circuit extending from including a front contact |50 of oscillator I80CT4, back contact |83 of relay IID, back contact |32 of relay IIHA, lower winding of relay 90C4, and back contact |34 of relay CEX4, to The picking up of that relay conditions a pick-up circuit for relay 90CA4 so that the shifting of contact |50 to its lower position will cause the picking up of such relay by the energization of a circuit extending from including back contact |50 of relay I80CT4, front contact |85 of relay 9004, and lower winding of relay 90CA4, to The relays 90C4 and 900Al1 are both maintained picked up by stick circuits comparable .to those which have been described with reference to other stepping relay banks until after the relay CEX4 has been picked up. Relay CEX4 is picked up when contact |50 of oscillator I80CT4 again shifts to its upper position upon the closing of a pick-up circuit extending from (-1-), including front contact I80CT4, back contact |83 of relay IID, back contactv |82 of relay IIHA, front contact |86 of relay 90CA4, and lower winding of relay CEX, to A stick circuit is closed at front contact |81 of relay CEX4 to maintain itl picked up during the restoration of the relays 90C4 and 90CA4 in a manner similar to that which has been described with reference` tothe control of other stepping relay banks.

In accordance with the stepping of the relay bank for the left-hand end of track section I2-I3Tuas it has been described, it is provided that every other impulse transmitted through the track circuit is of negative polarity in accordance with the energzation of the driven code transmitter relay |2CP during every other irnpulse by a circuit extending from (B including front contact |88 of relay 90C4, back contact |89 of relay 90CA4, back contact |54 of relay CEX4, winding of relay I2CP, and back contact of relay |2TA, t0 (CN).

In accordance with the reception of a 90 code at signal I3 (see Fig. 2F) the relay ISI-I is maintained energized, but the relay |3D is dropped away, because of the shifting of the code from a 180 toa 90 rate. It is therefore provided that, in accordance with the dropping away of relay |3D, the green lamp VI3Clrv of signal I3 is extinguished by the opening of front contact |62, and the yellow lamp I3Y of that signal is illuminated by the energization of a circuit closed from including front contact IGI of relay |3H, back contact |52 of relay |3D, and lamp I3Y, to

It is therefore provided that, upon entrance of a train into a siding section such as the section 8-9T, for example, the opposing leaving signal for the knext siding, such, for example, as signalIB, is put toV caution to warn any opposing control of signal G.

train that may be approaching such signal that there is an opposing train at the other end of the stretch of single track between the two sidings involved. It is further provided, as will be hereinafter described with reference to the passage of a west bound train, that protective indications are provided in a similar manner for the opposite direction of trafhc.

The approach of signal 8 by an east bound train causes the picking up of a stick relayV 8S for signal 8 in order to cause the transmission, after the train has passed out of track section 6- 1T as illustrated in Fig. 1D, of a 90 inverse code through the track section 5-'IT for the The transmission of such code through the track section 6--1T causes the signal 6 to display a caution indication, and, inasmuch as the code is at a 90 rate, it is provided that a 180 inverse code is transmitted through s the track section 4-5'1 to cause the clearing of signal Il as compared to the caution indication such signal t would display if the train A were proceeding in the opposite direction. inasmuch as the circuits by which such code transmission is effected are not shown,l a consideration will be here made as to the control of the stick relay 8S used in selecting the controls to be transmitted through the track section 6`|T, and the manner in which such controls can be transmitted will be apparent hereinafter upon considering the transmission of an inverse code through. the comparable track section |2- I3T after an each bound train has left such track section and entered the siding section I4-|5T.

The stick relay 8S is picked up upon the entrance of the train A into track section 6 -1T by the energization of a circuit extending from including normally closed contact 200 of the switch circuit controller for the track switch at the left-hand end of passing siding 24, back contact 20| of relay 1S, back contact 202 of relay 1TP, front contact 203 offrelay BTP, and wind-y ing4 of relay 8S, to The relay 8S is suiiiciently slow acting to be maintained picked up during the shifting of the contact 203 of relay ITPv upon the entrancey of the east bound train into track section 8-9T for the closing of a stick circuit extending from (-1-), including normally closed contact 200 of the switch circuit controller for the track switch at the left-hand end of track siding 2d, .back contact 20| of relay 1S, front contact 204' of relay 8S, back contact 203 of relay BTP, and winding of relay 8S, to Such stick i. circuit remains closed until the train A leavesv thetrack section 8 -9T to allow for the picking up Vof relay STP to open the stick circuit just described at back contact 203.

Under assumed operating conditions in which an east bound train A is occupying track section 8 -9T with the track layout in advance of the train unoccupied, the leaving signal I0 displays a clear indication in accordance with the reception of a inverse code as heretofore described. When the train A accepts the signal I0 and enters track section I0-I IT, the relays |0H and |0D are of course dropped away to cause the green lamp |0G of signal I0 to be extinguished by opening the circuit for such lamp at front contacts |38 and |39. The closing of back contact |38 of relay IOH closes an obvious circuit vto cause the illumination of the red lamp I 0R of signal I0.

4Upon ,the dropping away of the relay IOTP- picked upv by the energi-zation. of a circuit .ex--

tending from. includingifrontI contact 285 ot relay IGHP, back contact 2R35- of relay ISUTP", and.` winding'of relay IUS, to Such pickup.circuit is only momentarily closed because the relay* IGH is dropped away when the train enters the track section III-I IT, and the dropping away oi that relay opens on obvious circuit at front contact 20.1 for the slowv acting repeater relay IGI-IP which is sufficiently slow acting to provide for the picking up of the stick relay IS. Prior to the opening of the pick-up circuit for the stick relay IGS, a stick circuit is closed for such relay extending from (-I-), including back contact 281' of relay IOH, front contact 208 of relay IOS, and winding of relay IBS, to

The picking up of the relay IUS provides a means for selecting a code for transmission through the track section 8 -9T for the control of signal 8 which, at such signal location, denes the direction of the passage of the train A so as to provide less restrictive signal indications for a following train than would be provided if the train A were proceeding in the opposite direction through the track section Ill-IIT. It is therefore provided, that When the track section S-ST becomes unoccupied in the rear of the east bound train A, the code.

following track relays STA and STB (see Fig. 2B) at the right-hand end of siding 24 become active to follow a 180 driven code transmitted from the opposite end of the track section in a manner which has been described, it being assumed that the track layout is unoccupied in the rear of train A. The reception of such 180 driven code at the right-hand end of the siding 24 provides for the clearing of signal 9 in a manner which has been described to complete the restoration to normal of the conditions of that track section for the parts of the system affected by the transmission of a driven code.

Restoration to normal of the transmission of.

an inverse code through track section 8-9T, however, is not effected as the stick relay IOS has4 been picked up, and the track repeater relay IDTP is dropped away because of the presence..

of a train in the track, section III-IIT. It is therefore provided under` such conditions that a 90 inverse code is transmitted through the track section 8-9T because each cycle of operation of the stepping relay bank at the right-hand end of track section 8--9T includes successively the energization of the relays 9001, SIICA1 and CEXl.

More specifically, assuming the stepping relays to be momentarily deenergized at the end of a cycle of operation during an off period of the driven code received, the shifting of contact 58 (see Fig. 2B) of relay STB to its upper position upon the reception of the next on" period of the driven code causes the picking up of the relay 9001 (in accordance with the deenergized condition of the relay IGH) by the energization of a circuit extending from including front contact 58 of relay STB, backv Contact 59 of relay IlH, lower winding of relay 90C1, and back contact 289 of relay CEXl, to The picking up of that relay conditions a pick-up circuit for the relay 9(2CA1 so that such relay is picked up during the next off period of the driven code by the energizaticn of a circuit extending from (-1-), including back contact 58 of relay STB. front eramos?? duetothe presence oftlie train intrack section-y Contact, zill'ofrelay 9001;' andlowerfw-inding ci I0. I1IT, the stickA relay IIISfor signal I0iis relaySIiCAl, to Q With the stick` relay ISipieked up, a' circuit isuclosed v upontheV shifting' of Contact' 58i to its' upper position to'v cause" the picking up' of relay CEXl, extending from i-", including'front-conL tact "581J ofi relay aTB', back contact` 5% of` relay IIlH;` front contact 2H loi relay SOGAI, frontcorrtact 21I22 of relay'IS", and lower winding ofrelay CEXI, to

In accordance with the stepping of the relays SUCL, QGCAI and CEXas has been-described, it

is. provided that a-" inverse code isv transmitted' through the track made. up of` (-I) the oif periodsy of the driven code received at that end of the track section. Inasmuch as'th'e driven code received is at a rate, the compositionof the-inverse codev is such as to provide that each of the impulses of the inverse code isspaced from the next by a single blank period. Such spacing of' the impulsesA is effected because the transmissiony of each impulse is dependent upon tlre picking up of the code execution relay CEXl to close front contact 60 for conditioning the inverse code transmitter relay SCP so that it will be picked up upon the opening of front contact 61| of the code following relay STB. Relay CEXl, as has just been described, is pulsed at a 90 rate.

Upon receiving the 90 inverse code at the lefthand end of the passing siding 24, the contact G5 (see Fig. 2A) of relay BTA is pulsed at a 90 rate, and the pulsing of such relay causes the picking up of relay 8H in accordance with the energization of a circuit similar to that described for the energization of relay 9H. The pulsing of contact 65 of relay BTA also causes the picking up of relay 8HA because the circuit for such relay is tuned to a 90v rate. It is therefore provided that, if the approach lighting-'contact 86 of relay 'ITP were closed the yellow lamp of signal 8 would be illuminatedv for the display of a caution indication by the energization of a circui-t extending from (I-), including back contact 86 of relay I'TP, front contact 81 of: relay SH, back contact 88V of relay 8D, and the yellow lamp. SY of signal 8,' to

In. accordance with the energizatio-n of relay '8l-IA upon the reception of a 90' inverse code, it 1s provided4 that a 180 inverse code is transmitted section 8-9T, such code being through the; track section 6'-IT in a manner similar to that to be hereinafter describedwhen consideringv passage of the east bound train beyond .signal I4.

In accordance with' the general principles of absolute permissive block signaling systems, the entrance of an east bound'train Sinto track section I l IT causes the signals I-I and I3 to be conditioned to display stop indications. The relay'lIH (see Fig. 2D) is dropped away in accordance with the presence of the train in track section I D I IT because the pulsing ceases of the contacty l22, and the` dropping away -of that relay opens the circuit which has' been described for theyellow lamp IIY ofi signal II aty front contact |35fand conditions a circuit for the red lamp I IRwhic'h would be closed if the approach'lighting contact |3401" the approach repeater relay IZAPP were closed?, extending from (-I-), includingfr'ont contacty |34 of relay IZAPP, back contact I35.of relay I'IH; and lamp IIR, to

Inv accordance with the deenergized condition of vrelay'. I IH and the opposing stick relay I IS, it isinrovidedxthata carrier code made up of all impulses transmitted during` impulses is applied at the left-hand end of track section I2-I3T for transmission to the left-hand end of the siding 25.

The stepping relay bank at the left-hand end of trackI section I2-I3T (see Fig. 2E) is operative during the transmission of a driven code having all impulses in the same manner that has been described for the transmission of a 90 code through that track section in accordance with the deenergized condition of the relays IID and IIHA, and the impulses are applied to the track circuit I2-I3T in the same manner that has been described, except that a impulse is transmitted instead of a impulse each time the code execution relay CEX4 is picked up. That is, when the relay CEX4 is picked up for the transmission of every other on period of the driven code a circuit is closed for the negative energization of the code transmitter relay |2CP extending from (B includ- 'ing back `contact 2I5 of relay IIS, back contact |53 of relay III-I, front contact |54 of relay CEX4, Winding of relay I2CP,` and back contact |55 of relay |2TA, to (CN). The picking up of relay I2CP due to such energization causes its polar contact |51 to be in a right-hand position to effect thetransmission of a impulse by the energizatilon of a track 'circuit for track section I2--I3T that has been described.

At signal I3, in accordance with the reception of a' code composed of all impulses, the polar code following track relay I3TA (see Fig. 2F) ceases to 'be active, and the relay ISH is dropped away because of the inactivity of contact |80. The dropping away of that relay causes the extinguishing of the yellow lamp I3Y of signal I3 by the opening of front contact I 6I, and causes the illumination of the red lamp ISR of signal I3 upon the closing of an obvious circuit at back contact IBI.

The driven code received at signal I3, however, composed of all impulses, causes the pulsing of the contacts of the neutral code following track relay I3TB, and therefore causes .the operation of the stepping relays of the inverse code transmitter for the right-hand end of track section I2-I3T to elect the transmission of a 180 inverse code for the clearing of signal I2 in a manner which has been described. Inasmuch as the east bound train is assumed to occupy track section I-I IT, the approach lighting is effective to cause theillumination of the green lamp of signal I2 in accordance with the deenergized condition of the track repeater relay HTP (see Fig. 2E) to close back contact I'II).

The reception of the driven code composed of all characters at the right-hand end of track section I2-I3T causes the relay I3TP (see Fig. 2F) to remain picked up in accordance with the pulsing of contact 2I6, and the energized condition of such relay, with the relay ISI-I deenergized, provides for the transmission through the track section M`|5T of a 60 code in a manner similar to that which has been heretofore described under similar traffic conditions with reference to the approach of an east bound train tothe siding 24.

In accordance with. the trackway having been assumed to be clear in the rear of the train occupying track section III- l IT, the energized condition of relay 5D (see Fig. 2B) conditions the stepping relay bank at the left-hand end of track section I-IIT (see Fig. 2C) upon the closing of front contact |54 to provide for the energization of the code execution relay GEX2 each time vthe front Contact |03 of oscillator IIIEICT2 is closed. Thus, the closing of front contact I|6 of relay CEX2 at a 180 rate causes the application of a 180 driven code to the track section II'I--I IT in the rear of the east 'bound train occupying such track section in order to provide for proper restoration upon passage of the train into track section I2 I3T.

` The stick relay |2S (see Fig. 2E) for signal I2 is picked up upon the approach of such signal by an east bound train in accordance with the energization of a circuit extending from (-l-), including back contact 2I'I of relay TP, front contact 2I8 of relay I2H, and Winding of relay I2S, to The dropping away of relay IZH upon the shunting of its track section |2-I3T when the east bound train' passes signal. I2, closes a stick circuit for relay I2S extending from (-1-), including front contact 2|!! of relay I2S, back contact 2I8 of relay I 2H, and Winding of relay I2S, to y Assuming the east bound train to have left the track section Ill-I IT, the pulsing of contact |22 (see Fig. 2D) of relay IITA is again effected at a 180 rate to cause the picking up of the relays IIH and IID, but the picking up of relay IIH is delayed because of the inclusion in its circuit of back contact |23 of the stick relay I2S which is picked up at that time. The inclusion of back contact |23 of relay I2S in the circuit for relay III-I provides that the signal I| remains at stop to restrict the reversal of direction of the train occupying track section I2-I3T in accordance with the general principles of absolute permissive block signaling systems. The signal I I therefore is not conditioned to be cleared until the single stretch of track extending between the two sidings involved is entirely unoccupied.

In accordance with the deenergized condition of the relays |2H and I2D (see Fig. 2E) due to the presence of the east -bound train in track section |2|3T, the green lamp IZG of signal I2 is extinguished by the opening of front contact |72, and the red lamp IZR of signal I2 is illuminated when approach lighting is eiective for` such signal by the energization of an obvious circuit selected by the dropped away condition of the relay I2H at back contact I1 I.

The transmission of a 90 inverse code becomes effective through the track section I0|IT for the control of signal I0 in accordance with the energized condition of the stick relay IZS which has been picked up. Thus, the stepping is effective to cause the energization of the code execution relay CEX3 (see Fig. 2D) for the transmission of an impulse during every other oi period of the 180 driven code received in accordance with the deenergized condition of the relays IZHA and I2D. It is therefore provided that the closing of front contact |28 of relay IITB following an off period in which the stepping relays are all deenergized causes the relay SIIC3 to be picked up by the energization of a circuit extending from including front contact |23 of relay i ITB, back contact |29 of relay IED, back Contact 220 of relay IZHA, lower winding of relay C3, and back contact 22| of relay CEX3, to During the following off period of the driven code received, the relay Il0CA3 is picked up by the energization of a circuit extending from (i-), including back contact |28 of relay IITB, front contact 2220i relay 9003, and lower winding of relay 9iiCA3, to The picking up of relay BRCA1* conditions a pick-up circuit for the relay CEXfso that such relay is picked up upon the 

